Packers are used to temporarily separate two contiguous portions of a well or pipe from each other, for example in order to perform investigations or repairs in one of the portions.
One common type of packer an inflatable packer. Inflatable packers comprises an inflatable element carried by a support for inserting in the well or the pipe, the inflatable element being tubular having a circular section and having a wall that is leakproof, flexible and elastic, and deformable radially outwards under the action of the pressure of an internal fluid so as to bear hermetically against the wall of the well or the pipe to isolate one area of the well from another.
At rest, the diameter of the device and of the inflatable element is less than the diameter of the well or pipe. Once the packer has been positioned in the desired zone, the inflatable element is inflated by pumping in a liquid into the element, in particular water, a hydrocarbon, and/or the mud present inside the well or pipe. The fluid is raised to a high pressure, suitable for causing the inflatable element to expand and for pressing it firmly against the wall of the zone in question so as to close it hermetically in a temporary manner, isolating one portion of the borehole from the other. This prevents fluid flowing from between the two zones.
Once the investigation and/or repair operations have been completed, the inflatable element is deflated and the device is withdrawn. The packer can then be used again for closing a new zone of the same well or pipe, or it can be transferred to another site into a new well in order to perform the same function.
In an oil field application the inflatable element is generally about 1 m to 4 m long, with an initial outside diameter (i.e. when inflated) in the range of about 70 mm to 150 mm, and with a wall thickness (when not inflated) in the range of about 15 mm to 25 mm. The inflatable element is generally formed from a natural or synthetic elastomeric material such as rubber.
Appropriate installation of the inflatable element requires a relatively high internal pressure to be used to inflate the packer, for example about 30 megapascals (MPa) to 40 MPa. Therefore during inflation, the wall of the inflatable element is exposed to very large forces. The pressure difference between the inside and outside of the packer is very large and can go beyond the ability of the inflatable element to withstand, resulting in the packer expanding enormously and which can cause damage to the inflatable element, or even cause it to explode. Because of this the material forming the inflatable element is reinforced, often mechanically. WO93/12322 and WO2005003617 describe packers having mechanically reinforced inflatable element.
Generally wire-like reinforcing elements are used, such as at least one sheet of flexible strands, e.g. steel wires, embedded in the wall of the inflatable element, the sheet having a circularly cylindrical surface on the same axis as the inflatable element. It is also known to use a pair of concentric reinforcing sheets, each made up of a series of parallel flexible wires (or cables), e.g. made of steel, wound helically at a long pitch (i.e. at a small angle of inclination relative to the longitudinal axis of the device), the wires in the two layers having angles of inclination of similar size but of opposite directions. In a non-inflated inflatable element, the angle of inclination is initially about 15°, as the inflatable element is inflated the angle increases and reaches a final value of about 35° to 40°. In other packer devices, at least one similar third sheet (an auxiliary sheet) is provided disposed coaxially inside the other two sheets and is made of wires that are finer and closer together than the wires of the outer (main) sheets. The function of the auxiliary sheet is to oppose a phenomenon known as “extrusion” which is associated with the material constituting the wall of the inflatable element creeping outwards under the action of very high internal pressure, which runs the risk of forming a hernia passing through the gaps between certain reinforcing wires of the main sheets, and leading to the wall rupturing. This technique is relatively satisfactory, but does not completely eliminate the risk of the material being extruded or the corresponding risk of the inflatable element deteriorating.
This problem is resolved by providing a packer that includes at least one fiber layer, referred to as a “filter” layer which is circularly cylindrical in shape and disposed concentrically, being embedded in the wall of the material forming the inflatable element, inside relative to the sheets of flexible strands. The filter layer has a structure that acts as an anti-extrusion barrier, to limit creep of the material constituting the wall of the inflatable element and to prevent the material from passing outwards between the reinforcing strands under the effect of the pressure generated by the inflation fluid.
Current packers generally aim to minimize the risk of the inflatable element suffering from extrusion, splitting and concomitant rupturing. However these mechanical reinforcements for the packers do not completely prevent damage to the inflatable elements and in addition boreholes can have rough surfaces and the inflatable elements can also be damaged during their insertion into the well.
When damage occurs to the packer such as cracks in the material of the inflatable element this can create a path for the fluid to flow through the cables that are reinforcing the inflatable element, affecting the seal the packer is meant to create. If the pressure above the packer is greater than the pressure below the packer, fluid in the borehole can flow from above the packer to below the packer by migrating through the path created by the spaces in the steel cables, resulting in a leak between the top and bottom of the packers.
Therefore it is an object of the invention to provide a packer that will reduce the risk of fluid leaking if the material of the inflatable element is damaged. In particular a packer is provided where the spaces of the cables embedded in the elastic material forming the inflatable element are filled with a material to prevent fluid flow through the inflatable element of the packer when it is damaged.